This disclosure relates generally to display systems. More particularly, but not by way of limitation, this disclosure relates to a technique for tone mapping standard dynamic range (SDR) images for enhanced presentation on a high dynamic range (HDR) display element (e.g., for improved user experience).
Images conforming to the sRGB or ITU-R BT.709 standards are said to be SDR images. Both color spaces share the same white point (D65) and RGB chromaticity primaries, but can differ in their gamma value. The gamma response curve for sRGB follows a response curve with a gamma of 2.2 while the gamma value for BT.709 may vary from 2.2 to 2.4. SDR images, in the form of digital files such as (often 8 bit) .jpeg, .mov, or .web content are defined for viewing on SDR displays with typical black levels of around 0.1 cd/m2 (candela-per-meter-squared) and peak brightness levels of around 100 cd/m2, for a reference (dim) viewing environment. There is a current trend towards higher dynamic range displays such as provided by locally dimming backlight and liquid crystal displays (LCDs) and Organic Light Emitting Diode (OLED) displays, each of which can have black levels as low as 0.001 cd/m2 and peak brightness levels beyond 1000 cd/m2. To take advantage of these newer HDR displays, a technique is needed to convert legacy SDR images (including movies, photos and web content) into HDR content in a manner that generates “nice” images. That is, pleasing to a human viewer while preserving the artistic intent present in the original image.